Module java.base
Package java.util

Class GregorianCalendar

  • All Implemented Interfaces:
    Serializable,Cloneable,Comparable<Calendar>
    public classGregorianCalendarextendsCalendar
    GregorianCalendar is a concrete subclass ofCalendar and provides the standard calendar system used by most of the world.

    GregorianCalendar is a hybrid calendar that supports both the Julian and Gregorian calendar systems with the support of a single discontinuity, which corresponds by default to the Gregorian date when the Gregorian calendar was instituted (October 15, 1582 in some countries, later in others). The cutover date may be changed by the caller by callingsetGregorianChange().

    Historically, in those countries which adopted the Gregorian calendar first, October 4, 1582 (Julian) was thus followed by October 15, 1582 (Gregorian). This calendar models this correctly. Before the Gregorian cutover,GregorianCalendar implements the Julian calendar. The only difference between the Gregorian and the Julian calendar is the leap year rule. The Julian calendar specifies leap years every four years, whereas the Gregorian calendar omits century years which are not divisible by 400.

    GregorianCalendar implementsproleptic Gregorian and Julian calendars. That is, dates are computed by extrapolating the current rules indefinitely far backward and forward in time. As a result,GregorianCalendar may be used for all years to generate meaningful and consistent results. However, dates obtained usingGregorianCalendar are historically accurate only from March 1, 4 AD onward, when modern Julian calendar rules were adopted. Before this date, leap year rules were applied irregularly, and before 45 BC the Julian calendar did not even exist.

    Prior to the institution of the Gregorian calendar, New Year's Day was March 25. To avoid confusion, this calendar always uses January 1. A manual adjustment may be made if desired for dates that are prior to the Gregorian changeover and which fall between January 1 and March 24.

    Week Of Year and Week Year

    Values calculated for theWEEK_OF_YEAR field range from 1 to 53. The first week of a calendar year is the earliest seven day period starting ongetFirstDayOfWeek() that contains at leastgetMinimalDaysInFirstWeek() days from that year. It thus depends on the values ofgetMinimalDaysInFirstWeek(), getFirstDayOfWeek(), and the day of the week of January 1. Weeks between week 1 of one year and week 1 of the following year (exclusive) are numbered sequentially from 2 to 52 or 53 (except for year(s) involved in the Julian-Gregorian transition).

    ThegetFirstDayOfWeek() and getMinimalDaysInFirstWeek() values are initialized using locale-dependent resources when constructing a GregorianCalendar.The week determination is compatible with the ISO 8601 standard when getFirstDayOfWeek() isMONDAY and getMinimalDaysInFirstWeek() is 4, which values are used in locales where the standard is preferred. These values can explicitly be set by callingsetFirstDayOfWeek() andsetMinimalDaysInFirstWeek().

    Aweek year is in sync with aWEEK_OF_YEAR cycle. All weeks between the first and last weeks (inclusive) have the sameweek year value. Therefore, the first and last days of a week year may have different calendar year values.

    For example, January 1, 1998 is a Thursday. If getFirstDayOfWeek() isMONDAY and getMinimalDaysInFirstWeek() is 4 (ISO 8601 standard compatible setting), then week 1 of 1998 starts on December 29, 1997, and ends on January 4, 1998. The week year is 1998 for the last three days of calendar year 1997. If, however,getFirstDayOfWeek() isSUNDAY, then week 1 of 1998 starts on January 4, 1998, and ends on January 10, 1998; the first three days of 1998 then are part of week 53 of 1997 and their week year is 1997.

    Week Of Month

    Values calculated for theWEEK_OF_MONTH field range from 0 to 6. Week 1 of a month (the days withWEEK_OF_MONTH = 1) is the earliest set of at leastgetMinimalDaysInFirstWeek() contiguous days in that month, ending on the day beforegetFirstDayOfWeek(). Unlike week 1 of a year, week 1 of a month may be shorter than 7 days, need not start ongetFirstDayOfWeek(), and will not include days of the previous month. Days of a month before week 1 have aWEEK_OF_MONTH of 0.

    For example, ifgetFirstDayOfWeek() isSUNDAY andgetMinimalDaysInFirstWeek() is 4, then the first week of January 1998 is Sunday, January 4 through Saturday, January 10. These days have aWEEK_OF_MONTH of 1. Thursday, January 1 through Saturday, January 3 have aWEEK_OF_MONTH of 0. IfgetMinimalDaysInFirstWeek() is changed to 3, then January 1 through January 3 have aWEEK_OF_MONTH of 1.

    Default Fields Values

    Theclear method sets calendar field(s) undefined.GregorianCalendar uses the following default value for each calendar field if its value is undefined.

    GregorianCalendar default field values
    Field Default Value
    ERAAD
    YEAR1970
    MONTHJANUARY
    DAY_OF_MONTH1
    DAY_OF_WEEKthe first day of week
    WEEK_OF_MONTH0
    DAY_OF_WEEK_IN_MONTH1
    AM_PMAM
    HOUR, HOUR_OF_DAY, MINUTE, SECOND, MILLISECOND0

    Default values are not applicable for the fields not listed above.

    Example:

     // get the supported ids for GMT-08:00 (Pacific Standard Time) String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000); // if no ids were returned, something is wrong. get out. if (ids.length == 0)     System.exit(0);  // begin output System.out.println("Current Time"); // create a Pacific Standard Time time zone SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]); // set up rules for Daylight Saving Time pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000); pdt.setEndRule(Calendar.OCTOBER, -1, Calendar.SUNDAY, 2 * 60 * 60 * 1000); // create a GregorianCalendar with the Pacific Daylight time zone // and the current date and time Calendar calendar = new GregorianCalendar(pdt); Date trialTime = new Date(); calendar.setTime(trialTime); // print out a bunch of interesting things System.out.println("ERA: " + calendar.get(Calendar.ERA)); System.out.println("YEAR: " + calendar.get(Calendar.YEAR)); System.out.println("MONTH: " + calendar.get(Calendar.MONTH)); System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR)); System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH)); System.out.println("DATE: " + calendar.get(Calendar.DATE)); System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH)); System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR)); System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK)); System.out.println("DAY_OF_WEEK_IN_MONTH: "                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH)); System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM)); System.out.println("HOUR: " + calendar.get(Calendar.HOUR)); System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY)); System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE)); System.out.println("SECOND: " + calendar.get(Calendar.SECOND)); System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND)); System.out.println("ZONE_OFFSET: "                    + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000))); System.out.println("DST_OFFSET: "                    + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000))); System.out.println("Current Time, with hour reset to 3"); calendar.clear(Calendar.HOUR_OF_DAY); // so doesn't override calendar.set(Calendar.HOUR, 3); System.out.println("ERA: " + calendar.get(Calendar.ERA)); System.out.println("YEAR: " + calendar.get(Calendar.YEAR)); System.out.println("MONTH: " + calendar.get(Calendar.MONTH)); System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR)); System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH)); System.out.println("DATE: " + calendar.get(Calendar.DATE)); System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH)); System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR)); System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK)); System.out.println("DAY_OF_WEEK_IN_MONTH: "                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH)); System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM)); System.out.println("HOUR: " + calendar.get(Calendar.HOUR)); System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY)); System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE)); System.out.println("SECOND: " + calendar.get(Calendar.SECOND)); System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND)); System.out.println("ZONE_OFFSET: "        + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000))); // in hours System.out.println("DST_OFFSET: "        + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000))); // in hours

    Since:
    1.1
    See Also:
    TimeZone,Serialized Form

    • Field Detail

      • BC

        public static final int BC
        Value of theERA field indicating the period before the common era (before Christ), also known as BCE. The sequence of years at the transition fromBC toAD is ..., 2 BC, 1 BC, 1 AD, 2 AD,...
        See Also:
        Calendar.ERA,Constant Field Values

      • AD

        public static final int AD
        Value of theERA field indicating the common era (Anno Domini), also known as CE. The sequence of years at the transition fromBC toAD is ..., 2 BC, 1 BC, 1 AD, 2 AD,...
        See Also:
        Calendar.ERA,Constant Field Values

    • Constructor Detail

      • GregorianCalendar

        public GregorianCalendar()
        Constructs a defaultGregorianCalendar using the current time in the default time zone with the defaultFORMAT locale.

      • GregorianCalendar

        public GregorianCalendar​(TimeZone zone)
        Constructs aGregorianCalendar based on the current time in the given time zone with the defaultFORMAT locale.
        Parameters:
        zone - the given time zone.

      • GregorianCalendar

        public GregorianCalendar​(Locale aLocale)
        Constructs aGregorianCalendar based on the current time in the default time zone with the given locale.
        Parameters:
        aLocale - the given locale.

      • GregorianCalendar

        public GregorianCalendar​(TimeZone zone,Locale aLocale)
        Constructs aGregorianCalendar based on the current time in the given time zone with the given locale.
        Parameters:
        zone - the given time zone.
        aLocale - the given locale.

      • GregorianCalendar

        public GregorianCalendar​(int year,                         int month,                         int dayOfMonth)
        Constructs aGregorianCalendar with the given date set in the default time zone with the default locale.
        Parameters:
        year - the value used to set theYEAR calendar field in the calendar.
        month - the value used to set theMONTH calendar field in the calendar. Month value is 0-based. e.g., 0 for January.
        dayOfMonth - the value used to set theDAY_OF_MONTH calendar field in the calendar.

      • GregorianCalendar

        public GregorianCalendar​(int year,                         int month,                         int dayOfMonth,                         int hourOfDay,                         int minute)
        Constructs aGregorianCalendar with the given date and time set for the default time zone with the default locale.
        Parameters:
        year - the value used to set theYEAR calendar field in the calendar.
        month - the value used to set theMONTH calendar field in the calendar. Month value is 0-based. e.g., 0 for January.
        dayOfMonth - the value used to set theDAY_OF_MONTH calendar field in the calendar.
        hourOfDay - the value used to set theHOUR_OF_DAY calendar field in the calendar.
        minute - the value used to set theMINUTE calendar field in the calendar.

      • GregorianCalendar

        public GregorianCalendar​(int year,                         int month,                         int dayOfMonth,                         int hourOfDay,                         int minute,                         int second)
        Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale.
        Parameters:
        year - the value used to set theYEAR calendar field in the calendar.
        month - the value used to set theMONTH calendar field in the calendar. Month value is 0-based. e.g., 0 for January.
        dayOfMonth - the value used to set theDAY_OF_MONTH calendar field in the calendar.
        hourOfDay - the value used to set theHOUR_OF_DAY calendar field in the calendar.
        minute - the value used to set theMINUTE calendar field in the calendar.
        second - the value used to set theSECOND calendar field in the calendar.

    • Method Detail

      • setGregorianChange

        public void setGregorianChange​(Date date)
        Sets theGregorianCalendar change date. This is the point when the switch from Julian dates to Gregorian dates occurred. Default is October 15, 1582 (Gregorian). Previous to this, dates will be in the Julian calendar.

        To obtain a pure Julian calendar, set the change date toDate(Long.MAX_VALUE). To obtain a pure Gregorian calendar, set the change date toDate(Long.MIN_VALUE).

        Parameters:
        date - the given Gregorian cutover date.

      • getGregorianChange

        public final Date getGregorianChange()
        Gets the Gregorian Calendar change date. This is the point when the switch from Julian dates to Gregorian dates occurred. Default is October 15, 1582 (Gregorian). Previous to this, dates will be in the Julian calendar.
        Returns:
        the Gregorian cutover date for thisGregorianCalendar object.

      • isLeapYear

        public boolean isLeapYear​(int year)
        Determines if the given year is a leap year. Returnstrue if the given year is a leap year. To specify BC year numbers,1 - year number must be given. For example, year BC 4 is specified as -3.
        Parameters:
        year - the given year.
        Returns:
        true if the given year is a leap year;false otherwise.

      • equals

        public boolean equals​(Object obj)
        Compares thisGregorianCalendar to the specifiedObject. The result istrue if and only if the argument is aGregorianCalendar object that represents the same time value (millisecond offset from theEpoch) under the sameCalendar parameters and Gregorian change date as this object.
        Overrides:
        equals in class Calendar
        Parameters:
        obj - the object to compare with.
        Returns:
        true if this object is equal toobj;false otherwise.
        See Also:
        Calendar.compareTo(Calendar)

      • add

        public void add​(int field,                int amount)
        Adds the specified (signed) amount of time to the given calendar field, based on the calendar's rules.

        Add rule 1. The value offield after the call minus the value offield before the call isamount, modulo any overflow that has occurred infield. Overflow occurs when a field value exceeds its range and, as a result, the next larger field is incremented or decremented and the field value is adjusted back into its range.

        Add rule 2. If a smaller field is expected to be invariant, but it is impossible for it to be equal to its prior value because of changes in its minimum or maximum afterfield is changed, then its value is adjusted to be as close as possible to its expected value. A smaller field represents a smaller unit of time.HOUR is a smaller field thanDAY_OF_MONTH. No adjustment is made to smaller fields that are not expected to be invariant. The calendar system determines what fields are expected to be invariant.

        Specified by:
        add in class Calendar
        Parameters:
        field - the calendar field.
        amount - the amount of date or time to be added to the field.
        Throws:
        IllegalArgumentException - iffield isZONE_OFFSET,DST_OFFSET, or unknown, or if any calendar fields have out-of-range values in non-lenient mode.
        See Also:
        Calendar.roll(int,int),Calendar.set(int,int)

      • roll

        public void roll​(int field,                 boolean up)
        Adds or subtracts (up/down) a single unit of time on the given time field without changing larger fields.

        Example: Consider aGregorianCalendar originally set to December 31, 1999. Callingroll(Calendar.MONTH, true) sets the calendar to January 31, 1999. TheYEAR field is unchanged because it is a larger field thanMONTH.

        Specified by:
        roll in class Calendar
        Parameters:
        up - indicates if the value of the specified calendar field is to be rolled up or rolled down. Usetrue if rolling up,false otherwise.
        field - the time field.
        Throws:
        IllegalArgumentException - iffield isZONE_OFFSET,DST_OFFSET, or unknown, or if any calendar fields have out-of-range values in non-lenient mode.
        See Also:
        add(int,int),Calendar.set(int,int)

      • roll

        public void roll​(int field,                 int amount)
        Adds a signed amount to the specified calendar field without changing larger fields. A negative roll amount means to subtract from field without changing larger fields. If the specified amount is 0, this method performs nothing.

        This method callsCalendar.complete() before adding the amount so that all the calendar fields are normalized. If there is any calendar field having an out-of-range value in non-lenient mode, then anIllegalArgumentException is thrown.

        Example: Consider aGregorianCalendar originally set to August 31, 1999. Callingroll(Calendar.MONTH, 8) sets the calendar to April 30,1999. Using aGregorianCalendar, theDAY_OF_MONTH field cannot be 31 in the month April.DAY_OF_MONTH is set to the closest possible value, 30. TheYEAR field maintains the value of 1999 because it is a larger field thanMONTH.

        Example: Consider aGregorianCalendar originally set to Sunday June 6, 1999. Callingroll(Calendar.WEEK_OF_MONTH, -1) sets the calendar to Tuesday June 1, 1999, whereas callingadd(Calendar.WEEK_OF_MONTH, -1) sets the calendar to Sunday May 30, 1999. This is because the roll rule imposes an additional constraint: TheMONTH must not change when theWEEK_OF_MONTH is rolled. Taken together with add rule 1, the resultant date must be between Tuesday June 1 and Saturday June 5. According to add rule 2, theDAY_OF_WEEK, an invariant when changing theWEEK_OF_MONTH, is set to Tuesday, the closest possible value to Sunday (where Sunday is the first day of the week).

        Overrides:
        roll in class Calendar
        Parameters:
        field - the calendar field.
        amount - the signed amount to add tofield.
        Throws:
        IllegalArgumentException - iffield isZONE_OFFSET,DST_OFFSET, or unknown, or if any calendar fields have out-of-range values in non-lenient mode.
        Since:
        1.2
        See Also:
        roll(int,boolean),add(int,int),Calendar.set(int,int)

      • setWeekDate

        public void setWeekDate​(int weekYear,                        int weekOfYear,                        int dayOfWeek)
        Sets thisGregorianCalendar to the date given by the date specifiers -weekYear,weekOfYear, anddayOfWeek.weekOfYear follows theWEEK_OF_YEAR numbering. ThedayOfWeek value must be one of theDAY_OF_WEEK values:SUNDAY toSATURDAY.

        Note that the numeric day-of-week representation differs from the ISO 8601 standard, and that theweekOfYear numbering is compatible with the standard when getFirstDayOfWeek() isMONDAY and getMinimalDaysInFirstWeek() is 4.

        Unlike theset method, all of the calendar fields and the instant of time value are calculated upon return.

        IfweekOfYear is out of the valid week-of-year range inweekYear, theweekYear andweekOfYear values are adjusted in lenient mode, or anIllegalArgumentException is thrown in non-lenient mode.

        Overrides:
        setWeekDate in class Calendar
        Parameters:
        weekYear - the week year
        weekOfYear - the week number based onweekYear
        dayOfWeek - the day of week value: one of the constants for theDAY_OF_WEEK field:SUNDAY, ...,SATURDAY.
        Throws:
        IllegalArgumentException - if any of the given date specifiers is invalid, or if any of the calendar fields are inconsistent with the given date specifiers in non-lenient mode
        Since:
        1.7
        See Also:
        isWeekDateSupported(),Calendar.getFirstDayOfWeek(),Calendar.getMinimalDaysInFirstWeek()

      • computeFields

        protected void computeFields()
        Converts the time value (millisecond offset from theEpoch) to calendar field values. The time isnot recomputed first; to recompute the time, then the fields, call thecomplete method.
        Specified by:
        computeFields in class Calendar
        See Also:
        Calendar.complete()

      • toZonedDateTime

        public ZonedDateTime toZonedDateTime()
        Converts this object to aZonedDateTime that represents the same point on the time-line as thisGregorianCalendar.

        Since this object supports a Julian-Gregorian cutover date andZonedDateTime does not, it is possible that the resulting year, month and day will have different values. The result will represent the correct date in the ISO calendar system, which will also be the same value for Modified Julian Days.

        Returns:
        a zoned date-time representing the same point on the time-line as this gregorian calendar
        Since:
        1.8

      • from

        public static GregorianCalendar from​(ZonedDateTime zdt)
        Obtains an instance ofGregorianCalendar with the default locale from aZonedDateTime object.

        SinceZonedDateTime does not support a Julian-Gregorian cutover date and uses ISO calendar system, the return GregorianCalendar is a pure Gregorian calendar and uses ISO 8601 standard for week definitions, which hasMONDAY as theFirstDayOfWeek and4 as the value of theMinimalDaysInFirstWeek.

        ZoneDateTime can store points on the time-line further in the future and further in the past thanGregorianCalendar. In this scenario, this method will throw anIllegalArgumentException exception.

        Parameters:
        zdt - the zoned date-time object to convert
        Returns:
        the gregorian calendar representing the same point on the time-line as the zoned date-time provided
        Throws:
        NullPointerException - ifzdt is null
        IllegalArgumentException - if the zoned date-time is too large to represent as aGregorianCalendar
        Since:
        1.8